鲸鱼座A星49周围的解析分子气盘
A Resolved Molecular Gas Disk around the Nearby A Star 49 Ceti
摘要：
鲸鱼座49 A星，距离61 pc，在保留大量分子气体的同时表现出类似于碎片盘的尘埃性质是不寻常的。我们提出了解决的磁盘49 Ceti周围的亚毫米阵列在J=2-1旋转过渡的CO与分辨率为1.0x1.2角秒的观测。观测到的发射揭示了一个扩展的旋转结构，大约从侧面观察，并且在距离恒星约90 AU的距离内没有可检测到的CO发射。在2.1 mJy/束的3-sigma灵敏度下没有检测到1.3毫米连续发射。盘结构和化学模型表明，内盘没有分子气体，而距离恒星40至200 AU的外气体盘主要由恒星和星际辐射的光化学作用所控制。我们确定的模型，再现的空间分辨CO J=2-1发射，光谱能量分布，和未解决的CO J=3-2光谱的基本特征的参数。我们调查的磁盘化学和可观察到的性能的变化范围内的结构参数。[49]鲸鱼座似乎是一个罕见的例子，说明一个系统处于从富含气体的原行星盘到稀薄的、几乎不含气体的碎片盘之间的后期过渡阶段。
英文摘要：
The A star 49 Ceti, at a distance of 61 pc, is unusual in retaining a substantial quantity of molecular gas while exhibiting dust properties similar to those of a debris disk. We present resolved observations of the disk around 49 Ceti from the Submillimeter Array in the J=2-1 rotational transition of CO with a resolution of 1.0x1.2 arcsec. The observed emission reveals an extended rotating structure viewed approximately edge-on and clear of detectable CO emission out to a distance of ~90 AU from the star. No 1.3 millimeter continuum emission is detected at a 3-sigma sensitivity of 2.1 mJy/beam. Models of disk structure and chemistry indicate that the inner disk is devoid of molecular gas, while the outer gas disk between 40 and 200 AU from the star is dominated by photochemistry from stellar and interstellar radiation. We determine parameters for a model that reproduces the basic features of the spatially resolved CO J=2-1 emission, the spectral energy distribution, and the unresolved CO J=3-2 spectrum. We investigate variations in disk chemistry and observable properties for a range of structural parameters. 49 Ceti appears to be a rare example of a system in a late stage of transition between a gas-rich protoplanetary disk and a tenuous, virtually gas-free debris disk.
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